All 30 caliber is 7.62. A .308 is 7.62 x 51 - A 30-06 is 7.62 x 63 (.30 caliber of 1906) a 30-30 is 30 caliber with 30 grains of black powder, (back when they used black powder when the 30-30 was coined) - the AK-47 round is a 7.62 x 39 etc; etc; etc; When you are talking about the 7.62x51, it's just the NATO designation for the .308 Winchester. Taint rocket surgery.